Daily maintenance of pneumatic control valve

Daily maintenance of pneumatic control valve:

When the regulating valve uses graphite asbestos as the packing, lubricating oil should be added to the packing once every three months to ensure the flexibility and usability of the regulating valve. If the packing cap is found to be pressed very low, the packing should be replenished. If the PTFE dry packing is found to have hardened, it should be replaced in a timely manner; Attention should be paid to the operation of the pneumatic control valve during the patrol inspection, and the valve position indicator and regulator output should be checked for consistency; Regularly check the air source for regulating valves with locators and promptly address any issues found; Regularly maintain the hygiene of the regulating valve and ensure that all components are intact and functional. Products from Shanghai Shenghe can be purchased from all over the country. We offer 24-hour after-sales service and technical support. If needed, please feel free to call our customer service hotline or directly contact our customer service representative or engineer. Welcome to browse our company website

Pneumatic control valve is one of the widely used instruments in petrochemical enterprises. Its accurate and normal operation is of great significance for ensuring the normal operation and safe production of process equipment. Therefore, it is necessary to strengthen the maintenance of pneumatic control valves.

1¡¢ Key inspection areas during maintenance

Check the inner wall of the valve body: In situations with high pressure difference and corrosive media, the inner wall of the valve body and the diaphragm of the diaphragm valve are often impacted and corroded by the media, and it is necessary to focus on checking the pressure and corrosion resistance;  

Check the valve seat: Due to the infiltration of the medium during operation, the threaded inner surface used to fix the valve seat is prone to corrosion, causing the valve seat to loosen;  

Check the valve core: The valve core is one of the movable components of the regulating valve, which is severely eroded by the medium. During maintenance, it is necessary to carefully check whether all parts of the valve core are corroded or worn, especially under high pressure differentials. The wear of the valve core is more severe due to cavitation caused by cavitation. Severely damaged valve cores should be replaced; Check the sealing packing: Check whether the asbestos rope of the packing is dry. If polytetrafluoroethylene packing is used, pay attention to checking whether it is aging and whether its mating surface is damaged;  

Check if the rubber film in the actuator is aging and if there are any cracks.  

2¡¢ Daily maintenance of pneumatic control valve

When the regulating valve uses graphite asbestos as the packing, lubricating oil should be added to the packing once every three months to ensure the flexibility and usability of the regulating valve. If the packing cap is found to be pressed very low, the packing should be replenished. If the PTFE dry packing is found to have hardened, it should be replaced in a timely manner; Attention should be paid to the operation of the regulating valve during the patrol inspection, and the valve position indicator and regulator output should be checked for consistency; Regularly check the air source for regulating valves with locators, and promptly address any issues found; Regularly maintain the hygiene of the regulating valve and ensure that all components are intact and functional.  

3¡¢ Common faults and their causes

£¨1£© The regulating valve does not operate. The fault symptoms and causes are as follows:

1. No signal, no gas source. ¢Ù The gas source is not turned on, ¢Ú due to the water content in the gas source freezing in winter, the air duct is blocked or the filter and pressure reducing valve are blocked and malfunctioning, ¢Û compressor failure; ¢Ü The gas source main pipe is leaking.  

2. There is a gas source but no signal. ¢Ù Regulator malfunction, ¢Ú signal tube leakage; ¢Û The locator bellows is leaking air; ¢Ü Adjust the damage of the omentum plate.  

3. The locator has no air source. ¢Ù Filter blockage; ¢Ú Pressure reducing valve malfunction I ¢Û Pipeline leakage or blockage.  

4. The locator has a gas source but no output. The throttle hole of the locator is blocked.  

5. There is a signal but no action. ¢Ù Valve core detachment, ¢Ú valve core jamming with society or valve seat; ¢Û The valve stem is bent or broken; ¢Ü The valve seat and valve core are frozen or contaminated with coke blocks; ¢Ý The actuator spring has rusted due to long-term disuse.  

£¨2£© The action of the regulating valve is unstable. The fault symptoms and causes are as follows:

1. Unstable gas source pressure. ¢Ù The compressor capacity is too small; ¢Ú Pressure reducing valve malfunction.  

2. The signal pressure is unstable. ¢Ù The time constant (T=RC) of the control system is inappropriate; ¢Ú The regulator output is unstable.  

3. The gas source pressure is stable, and the signal pressure is also stable, but the action of the regulating valve is still unstable. ¢Ù The ball valve of the amplifier in the locator is not tightly closed due to dirt wear, and when the air consumption increases significantly, it will produce output oscillation; ¢Ú The nozzle baffle of the amplifier in the locator is not parallel, and the baffle cannot cover the nozzle; ¢Û Leakage of output pipes and wires; ¢Ü The rigidity of the executing mechanism is too low; ¢Ý The friction resistance is high during the movement of the valve stem, and there is obstruction at the contact area.  

£¨3£© Adjust valve vibration. The fault symptoms and causes are as follows:

1. The regulating valve vibrates at any opening. ¢Ù Unstable support; ¢Ú There is a vibration source nearby; ¢Û The valve core and liner are severely worn.  

2. The regulating valve vibrates when approaching the fully closed position. ¢Ù The regulating valve is too large and is often used at a small opening; ¢Ú The flow direction of the medium in a single seat valve is opposite to the closing direction.  

£¨4£© The action of the regulating valve is sluggish. The phenomenon and reasons for sluggishness are as follows:

1. The valve stem is only sluggish when moving in one direction. ¢Ù Membrane damage and leakage in pneumatic membrane actuator; ¢Ú The "O" seal in the actuator leaks.  

2. The valve stem exhibits sluggishness during reciprocating motion. ¢Ù There is adhesive blockage inside the valve body; ¢Ú Deterioration and hardening of polytetrafluoroethylene fillers or drying of lubricating oil with graphite asbestos fillers; ¢Û Adding too much filler increases frictional resistance; ¢Ü Due to the non straight valve stem, there is high frictional resistance; ¢Ý Pneumatic control valves without locators can also cause sluggish operation.  

£¨5£© The leakage of the regulating valve increases. The reasons for the leakage are as follows:

When the valve is fully closed, there is a large amount of leakage. ¢Ù The valve core is worn and has severe internal leakage, and the valve is not properly adjusted and cannot be tightly closed.  

2. The valve cannot reach the fully closed position. ¢Ù The pressure difference of the medium is too large, the rigidity of the actuator is small, and the valve is not tightly closed; ¢Ú There are foreign objects inside the valve; ¢Û Lining sintering.  

£¨6£© The adjustable range of traffic becomes smaller. The main reason is that the valve core is corroded and becomes smaller, thereby increasing the adjustable minimum flow rate.  

Understanding the faults and causes of pneumatic control valves can enable targeted measures to be taken to solve them.